Electric actuator

ABSTRACT

An electric actuator having an in-line rotation shaft, electric motor and encoder in which the encoder shaft, the motor shaft and the rotation shaft is concentric and integrally formed.

This application claims the benefit of Provisional Application SerialNo. 60/264,330, filed Jan. 26, 2001

BACKGROUND OF THE INVENTION

1. Field of the Art

The present invention relates generally to an electrically poweredlinear actuator and more particularly to an electrically poweredactuator having an inline, direct motor mount and adapted for a varietyof robotic or other applications. The invention has particularapplication to the control of robotic, pedestal or fixture welding gunsand specifically, welding guns utilized in the automotive industry. Theinvention also has application to the actuation of clamping fixtures andthe like in various industries such as the automotive industry.

2. The Prior Art

Various industries, and particularly the manufacturing industry, haveutilized linear actuators to control the movements of automated weldingguns, automated clamping fixtures, and the like. Specifically, in theautomotive industry, actuation and control of welding guns and clampingfixtures has been accomplished using fluid actuators such as pneumaticor hydraulic actuators. While fluid actuators have functioned reasonablywell for this purpose, they inherently embody various limitations. One,because of the possibility of leaks and failure of seals, etc. in thefluid actuators, there is always the concern of contamination of theworksite by a leaking fluid. Second, fluid actuators necessarily requirea source of pressurized fluid and a fluid supply system. This leads tosignificant maintenance and other costs.

Accordingly, there is a need in the art for an improved actuator whichovercomes the deficiencies and limitations of the prior art, and inparticular, an improved actuator which is designed for use incontrolling the movement of, and accommodating the loads associatedwith, welding guns, clamping fixtures and the like, such as those usedin the automotive industry.

SUMMARY OF THE INVENTION

In contrast to the prior art, the present invention relates to anelectric actuator having particular application to the actuation ofwelding guns, clamping fixtures or the like, and more particularly tothe actuation of welding guns and clamping fixtures for use in theautomotive manufacturing industry. In contrast to the fluid actuators ofthe prior art, the present invention provides an electrically poweredin-line actuator which overcomes the limitations of the prior fluidactuators.

To minimize downtime and infra structure changes and the like during achangeover from existing fluid actuators to the electrically poweredactuator of the present invention, the actuator of the present inventionhas been designed to fit within the same space or package and to be noheavier than existing fluid actuators, while at the same time providingat least comparable speed, thrust and range of movement. This isaccomplished by utilizing a ball or roller screw electric actuatorconcept and by mounting the actuating motor in-line and directly to theactuator drive shaft. To provide additional advantages for maintenanceor repair, the electric actuator of the present invention has also beendesigned to be comprised of a modular construction, thereby facilitatingeasy disassembly and substitution or repair of modular components.

To provide positioning accuracy to the actuator, a rotary or othersimilar encoder is provided. Like the motor, this encoder is providedin-line and in direct connection with the actuator drive shaft.

The actuator of the present invention also includes a means andmechanism for manually overriding the electrically powered actuator inthe event of a loss of electrical power, actuator jamming or otheractuator malfunction and a mechanism for enabling the actuator headand/or end cap to be rotated or mounted in a variety of differentpositions and/or configurations to accommodate different welding,clamping or actuation environments. In a preferred embodiment, alubrication assembly is provided for insuring sufficient actuatorlubrication and thus a reduction in maintenance. Means are also providedfor accommodating the various loads (such as side loads) which arecommon with the actuation for welding guns and the like.

Accordingly, it is an object of the present invention to provide animproved actuator for welding guns, clamping fixtures and the like andmore particularly for welding guns and clamping fixtures utilized in theautomotive manufacturing industry.

Another object of the present invention is to provide an improvedelectrical actuator which can replace the conventional fluid actuatorsof the automotive manufacturing industry without sacrificing size orweight restrictions, while still maintaining comparable thrust, speed,range of movement and load accommodation.

A further object of the present invention is to provide an electricactuator having an in-line, direct motor mount and a manual override.

Another object of the present invention is to provide an electricactuator that eliminates or minimizes impact loading as the thrust tubereaches its innermost travel position.

Another object of the present invention is to provide an in-lineelectrical actuator in combination with an improved axial bearingretaining means.

A further object of the present invention is to provide an electricactuator with a thrust assembly bearing combination to resist side loadsand to isolate the roller screw from any such side loads.

A still further object of the present invention is to provide anelectrical actuator for use in the automotive manufacturing industrywhich provides for universal mounting arrangements.

A still further object of the present invention is to provide alubrication system for the actuator.

These and other objects of the present invention will become apparentwith reference to the drawings, the description of the preferredembodiment and the appended claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric, exploded view of the actuator of the presentinvention.

FIG. 2 is a view, partially in section, of the actuator in accordancewith the present invention as viewed along a plane extending along andthrough the longitudinal axis of the actuator.

FIGS. 3, 4 and 5 are isometric views of the bearing plate at theproximal end of the motor showing different orientations and positionsfor the electrical supply.

FIG. 6 is a view, partially in section and similar to FIG. 2, showing aportion of the actuator with the tube assembly in a partially extendedposition.

FIG. 7 is a fragmentary, partially exploded view, partially in section,of the means to relieve impact loading as the thrust tube reaches itsinnermost position.

FIG. 8 is a fragmentary view, partially in section, of the thrust tubeand the means for relieving impact loading as the thrust tube reachesits innermost position.

FIG. 9 is a view, partially in section, as viewed along the line 9—9 ofFIG. 2.

FIG. 10 is an isometric view of a further embodiment of the actuator ofthe present invention showing a modified power supply end.

FIG. 11 is an isometric, exploded view of a further embodiment of anactuator in accordance with the present invention showing a furthermanual override mechanism.

FIG. 12 is a view, partially in section, showing the override mechanismof FIG. 11.

FIG. 13 is an exploded, fragmentary isometric view showing portions ofthe override gear of FIGS. 11 and 12.

FIG. 14 is a view, partially in section, as viewed along the line 13—13of FIG. 10.

FIG. 15 is an isometric, exploded view showing the motor and bearingassembly and a portion of the thrust assembly.

FIG. 16 is an electrical side view showing a welding apparatus inaccordance with the present invention comprising an electric actuator asdescribed herein in combination with a welding gun.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention provides an improved actuator for use in providingcontrolled and accurate linear movement to a work piece. Although theactuator of the present invention has applicability to a variety of workpieces and in a variety of industries, it has particular application tothe actuation of welding guns, clamping fixtures and the like for use inthe automotive manufacturing industry. Accordingly, the preferredembodiment will be described with respect to the application of thepresent invention to welding guns, clamping fixtures or the like,without any implication that the present invention is limited to thatapplication.

In describing the preferred embodiment of the present invention,reference is first made to FIGS. 1, 2 and 15 comprising exploded andsectional views of the actuator or portions thereof. In general, theactuator of the present invention is an electrically powered, in-lineactuator in which the electric motor powering means is connecteddirectly to, and in-line with, the roller or lead screw of the actuator.In describing the actuator of the present invention, the terms“proximal” and “distal” are used to define directions/orientationsrelative to the actuator. Specifically, the term “proximal” shall meantoward the encoder or motor end of the actuator while the term “distal”shall mean toward the work piece connection end. In general, theactuator includes a motor or rotational motion generating section 12, aproximal or control and electric power supply end 14 and a distal orthrust and work piece connection end 16 (FIG. 2).

The motor section 12 is positioned between the ends 14 and 16 andincludes an outer motor housing 18, a bearing plate or block 24 at itsproximal end and a bearing plate or block 26 at its distal end.Positioned within the housing 18 is an electric motor 28 withconventional electric motor windings and other functional elements 20and a motor drive shaft 22. The motor drive shaft 22 is centrallypositioned within the housing 18 along the longitudinal axis 13 of theactuator and extends between the bearing blocks 24 and 26. The motorshaft 22 includes a distal end portion 30 which is rotatably supportedwithin the bearing block 26 by the bearing 34 and a proximal end portion32 which is rotatably supported by the bearing 38 in the bearing block24. Both of the shaft portions 30 and 32 are integrally formed with andcoaxial or in-line with the drive shaft 22 along the longitudinal axis13. Further, as will be described below the shaft portion 30 isintegrally formed with a threaded roller screw 36 and the shaft portion32 is integrally formed with an encoder shaft extension 40 to support arotary encoder 77.

As shown in the drawings, the motor shaft 22, the roller screw 36 andthe encoder shaft extension 40 are concentric, inline and integrallyformed from a single piece of shaft stock. Accordingly, at least allaxial movement of or loads against the thrust tube 56 and the thrusttube assembly 46 is resisted by the screw 36. Because any axial movementof the shaft extension 40 and thus the encoder 77, beyond minimaltolerances, will tend to adversely affect the encoder 77 and theaccuracy thereof, the shaft 36 must be axially captured relative to thehousing 42 and the bearing block 26 to prevent or minimize any suchmovement.

To axially capture the screw 36 relative to the bearing block 26, thebearing 34 is press fit onto the shaft portion 30 so that its distalaxial edge engages a bearing stop 103 which is integrally formed in theshaft portion 30. The proximal axial edge of the bearing 34 is securedrelative to the bearing block 26 by a bearing retaining plate 63. Asshown best in FIGS. 2, 9 and 15, the bearing plate 63 has a generallyannular configuration and is rigidly connected to the bearing block 26by plurality of threaded screws 67. Unlike conventional bearingretaining rings, washers or the like which permit some limited axialmovement of the bearing and thus the shaft on which it is mounted, thebearing plate 63 connected to the bearing block 26 by the screws 67 toaxially capture the screw 36 relative to the block 26 and to prevent orminimize any axial movement thereof, beyond minimal acceptabletolerances. This assures accuracy of the encoder 77.

The thrust section 16 of the actuator 10 includes a thrust tube housing42 and a thrust tube head 44. The thrust tube housing 42 is rigidlyconnected between the bearing block 26 and the head 44 by a plurality ofelongated threaded members 23 and 47 to define an internal thrust tubechamber 48. As shown in FIG. 1, four cap screws 23 extend through thefour corner holes 27 in the bearing block 24 and the four corner holesin the bearing block 26 and into corresponding threaded holes 33 in thetube housing 42. Similarly, four cap screws 47 extend through the fourcorner holes 37 in the tube head 44 and into corresponding threadedholes (not shown) in the housing 42.

Each of the bearing blocks 26 and the tube head 44 is provided with aplurality of mounting holes 53 to mount the actuator relative to a fixedsupport (not shown). Although mounting holes 53 are shown on only twosides of the bearing block 26 and tube head 44, such mounting holes canbe provided on all four sides to provide maximum mounting flexibility.Alternate mounting holes 57 (FIG. 2) are also provided in the endsurface of the tube head 44. These mounting holes 57 are internallythreaded and extend axially relative to the longitudinal axis 13.

As shown, the housing 42 is elongated, is generally parallel to thelongitudinal axis 13 of the actuator and includes a plurality ofsidewalls 43. The length of the housing 42 may vary depending on thedesired movement range or function of the actuator. The housing 42, andthus the interior of the thrust chamber 48, has a square or multi-sidedcross-sectional configuration. Although the housing may be constructedof a variety of materials, it is preferably extruded and constructed ofa lightweight metal or metal alloy such as aluminum.

Positioned within the chamber 48 is a thrust tube assembly 46 whichincludes a roller screw nut 50, a roller screw coupler 52, a bearing orguide means 54 and a thrust tube 56. As illustrated best in FIGS. 2 and6, the roller screw shaft or lead screw 36 extends from the motor shaft22, through the tube assembly 46 and toward the head 44. The rollerscrew 36 is provided on its outer surface with continuous threads and,in the preferred embodiment, is integrally formed with and in axialalignment with the motor shaft 22 and its distal extension 30. Thus, thescrew 36 rotates with the motor shaft 22. A compressible bumper 58 andimpact loading relief assembly as described below are connected to thedistal or outer end of the roller screw 36 by a screw 60 or otherthreaded member. The roller screw 36 is unsupported at its free endother than by the internal wall of the thrust tube 56.

The impact loading relief assembly for the actuator of the presentinvention is shown generally in FIG. I and more specifically in FIGS. 7and 8. This assembly includes the compressible bumper 58 and theplurality or rings or disc members 106, 108, 109 and 110. Duringoperation of the actuator, the roller screw 36 rotates in one directionor the other to result in corresponding axial movement of the thrusttube 56 and thus the thrust rod end 62. During this axial movement, thethrust tube 56 and end 62 remain rotationally fixed. As the thrust tube56 and the end 62 reach their innermost, retracted position, therotating screw 36 and its associated impact relief assembly will oftenengage the inner end of the thrust rod end 62 as shown in FIG. 8.Because the connection end 62 is rigidly secured to the screw nut 50which is threadedly received on the screw 36, any rotation of the shaft36 after such initial engagement causes the end 62 to be pulled tightertoward the shaft 35 with the compressible bumper or cushion 58sandwiched therebetween. In the preferred embodiment, this compressiblematerial is urethane. Thus, the bumper 58 functions to relieve the axialcomponent of any impact loading between the end 62 and the screw 36.

The rotational component of impact loading between the screw 36 and thethrust tube 56 and end 62 is caused by the continued limited rotation ofthe screw 36 after initial engagement. This rotational component ofimpact loading is relieved by means which permits limited rotationalmovement between the screw 36 and the bumper 58. In the preferredembodiment, this means includes the pair of steel rings or discs 106 and109 positioned on opposite sides of a self-lubricating, low frictionring or disc 108 at the proximal end of the bumper 58. Preferably, thering 108 is constructed of a self-lubricating brass material commonlyreferred to as oilite. A further ring or disc 110 is positioned at thedistal end of the bumper 58 as shown so that the bumper 58 is sandwichedbetween the washers 109 and 110. A tube or sleeve 111 is positioned overthe threaded member 60 to support the rings 106, 108, 109, 110 and thebumper 58 as shown. The screw 60 is threadedly received by the distalend of the screw 36 as shown. During impact loading, the proximal edgesurface of the thrust rod end 62 engages the ring 110.

Accordingly, it can be seen that the impact loading relief assembly ormeans in accordance with the present invention includes a means forrelieving both the axial and rotational components of impact loading asthe thrust tube reaches its innermost proximal position. Although themeans for relieving the axial component is shown as the urethane bumper58, this can include other compressible structure which permits limitedaxial movement of the end 62 relative to the threaded screw 36 afterimpact. Similarly, although the preferred embodiment discloses the lowfriction disc 108 sandwiched between the discs 106 and 109 as the meansfor relieving the rotational component of impact loading, such means canbe comprised of various other structures such as a variety of bearingmembers which permit limited rotational movement of the threaded screw36 relative to the bumper 58 or other axial relief means after impact.Further, although the preferred embodiment shows the impact loadingrelief assembly as being threadedly received in the end of the screw 36,it could also be threadedly received in the end 62.

The roller screw nut 50 is a conventional roller screw nut having aplurality of planetary or peripherally positioned roller screws. Duringoperation of the actuator, these planetary roller screws engage theouter threads of the roller screw shaft 36 and remain rotationally fixedrelative to the housing 42 to convert the rotational movement of theshaft 36 into axial movement of the thrust tube assembly 46. Thus, theassembly 46 moves axially between a retracted position shown in FIG. 2and various extended positions such as that shown in FIG. 6. Rollerscrew nuts 50 of the type usable in the preferred embodiment of thepresent invention are available commercially such as roller screw nutsprovided by Rollvis of Switzerland or SKF of Japan, among others. Thecoupler 52 is rigidly secured to the roller screw nut 50 and functionsto rigidly secure the nut 50 to the inner or proximal end of the thrusttube 56. The outer or distal end of the thrust tube 56 is provided witha thrust rod end 62. The rod end 62 is rigidly connected to the thrusttube 56 by threads or other appropriate means and includes a connectionend 64 such as a threaded connection or the like, for connection to awork piece. In the preferred embodiment, the work piece could be awelding gun, a clamping fixture or the like. The thrust tube 56 isguided and supported for axial movement relative to the head 44 by thebearing 66 positioned between a portion of the head 44 and externalsurface of the thrust tube 56.

The bearing 54 which guides axial movement of the thrust assembly withinthe housing 42 is rigidly connected to the roller screw coupler 52 asshown in FIGS. 1, 2 and 15. The bearing 54 extends around the entireperiphery of the coupler 52 and is positioned between the coupler 52 andthe inner surface of the thrust tube housing 42 for the purpose ofguiding the thrust tube assembly 46 axially along the roller screw shaftwithin the chamber 48. As shown best in FIGS. 1, 2 and 15, the bearing54 is comprised of four individual bearing members 54(a-d) havinggenerally flat exterior guide surfaces to engage the inner,longitudinally extending flat surfaces of the four sidewalls 43 of thethrust tube housing 42 and to prevent rotation of the thrust tubeassembly 46 as the roller screw 36 rotates. The individual bearingmembers of the bearing 54 are preferably constructed of Delron or othersynthetic, low friction material. The bearing 54 in combination with thebearing 66, which is also preferably constructed of a low friction,synthetic bearing material, functions to capture the axially moveablethrust assembly 46 relative to the housing 42 and to resist side loadforce on the distal end of the tube 56 during operation. Thus, with thisbearing combination, the roller screw 36 is isolated from any sideloading on the distal end of the tube 56 or any other portion of theassembly 46. This is particularly important for a linear actuator whichis intended for use in an environment where the possibility ofsignificant side loads exist, such as the actuation of welding guns,clamping fixtures or the like.

As shown best in FIGS. 1, 2 and 6, a lubrication assembly is providedfor lubricating the roller screw nut 50 and the roller screw shaft 36during use. This assembly includes a lubrication delivery tube in theform of the coiled, flexible tube 68. The coiled tube 68 extends betweena lubrication port 73 (FIG. 1) in the wall of the thrust tube housing 42and a lubrication port 76 (FIGS. 2 and 6) in the roller screw nut 50.The tube 68 is provided with lubrication fittings 72 and 70 at its endsfor operative connection with the lubrication ports 73 and 76,respectively. The lubrication fitting 72 which connects with the port 73may be provided with a zerk or other fitting for periodic manuallubrication or can be provided with a continuous supply of lubricationfor automatic lubrication of the roller screw nut 50 and roller screwshaft 36. The coiled delivery tube 68 enables the roller screw nut 50and the entire thrust assembly 46 to move reciprocally within the thrustchamber 48 along the roller screw shaft 36 (as shown in FIGS. 2 and 6)while maintaining lubrication during the entire such movement. Ifautomatic lubrication is desired, a lubrication pump 74 may be providedto supply grease or other lubrication to the tube 68 through alubrication supply tube 75 connected with the fitting 72. The pump 74may be connected with a lubrication reservoir 71 via the supply line 79,with the operation of the pump 74 controlled by a controller 81. In somecases, the tube 68 can be eliminated. In these cases, lubrication ispacked into the interior of the nut 50 through the port 76 prior to use.

The proximal or control and power supply end 14 of the actuator includesan extension 40 of the motor shaft 22 and a rotary encoder 77 mounted tothe shaft extension 40. The rotary encoder 77 is a conventional rotaryencoder which includes a pair of connection tabs or ears 91 forconnecting the encoder 77 to the bearing plate 24. In the preferredembodiment, the shaft extension 40 is integrally formed with and isaxially aligned with the proximal shaft portion 32 and thus the motorshaft 22. In the embodiment shown in FIGS. 1-5, a further shaftextension 92 extends outwardly from the proximal end surface of theencoder 77. This further extension 92 is integrally formed with theextension 40 and thus the main motor shaft 22 and is aligned with theaxial center of the shaft 22 and the extension 40. Preferably, theextension 92 is provided with a hexagonal end or a pair of flats orother rotation means to provide a manual rotation mechanism or overridefor the shaft 22. This manual override permits the motor shaft 22 andthus the roller screw shaft 36 to be manually rotated if necessary ordesired. This need might arise in the event of a power outage, amalfunction of the actuator or power system or when the system becomeslocked (i.e., the screw 36 driven against the end 62) at the end of thestroke.

A cover 93 is connected with the proximal end of the bearing plate 24.The cover 93 has a generally hollow interior to define a chamber 76(FIG. 2) to house the encoder 77 and the electrical power supply wires78 (FIGS. 3, 4 and 5) and to keep such elements free from dust and othercontaminants. As shown best in FIG. 1, the cover 93 is provided with aplurality of connection openings 80. These openings 80 are aligned withcorresponding threaded openings 82 in the bearing plate 24. Threadedmembers 83 extend through the openings 80 and are received by thethreaded openings 82 to secure the cover 93 to the bearing plate 24. Inthe preferred embodiment, the position of the openings 80 and 82 aresymetrically positioned. This enables the cover 93 to be connected withthe bearing plate 24 in several (at least three) different rotationalpositions. One edge of the cover 93 is provided with one or moreelectrical access openings 84 to provide electrical power to the motor28 and communicate control signals between the encoder and a controlmeans (not shown).

As illustrated best in FIGS. 3, 4 and 5, electrical power and actuatorcontrol signals are communicated to and from the encoder 77 and themotor 28 via the plurality of electrical leads or wires 78. These leads78 are provided to the motor 28 through the electrical port 86 in thebearing plate 24. The ends of the leads 78 are mounted to a connector 88which is in turn connected with the cover 93 at one of the electricalaccess openings 84. The leads 78 between the electrical port 86 and theconnector 88 are preferably coiled such as is shown in FIGS. 3, 4 and 5to permit the cover 93 to be connected to the bearing plate 24 in anyone of at least three rotational positions through an angle of about270°. With this connection flexibility, a single actuator can bemodified or adjusted to fit a variety of different power supplypositions merely by rotating the cover 93.

A motor shaft access cover 90 provides rotational access to the shaftextension 92 through an opening 94 in the cover 93. The access cover 90is preferably provided with exterior threads to be received by internalthreads in the cover 93 and is designed for selective manual rotationand thus removal. When removed, access is provided to the shaftextension 92 through the opening 94 so that the extension 92 and theentire motor shaft 22 and roller screw shaft 36 can be manually rotatedby a wrench or other tool if desired.

With the structure in accordance with the present invention, axialmovement of the fixture connection end 64 of the thrust tube assembly46, and thus the welding gun or other fixture attached thereto, can beprecisely and accurately controlled by rotation of the motor shaft 22.As the motor shaft 22 and thus the roller screw shaft 36 rotates in afirst rotational direction, this rotational movement is converted to anaxial movement of the thrust tube assembly 46 and thus the fixture end64 and attached fixture in a first axial direction such as from theretracted position shown in FIG. 2 to the partially extended positionshown in FIG. 6. Such axial movement is along the longitudinal axis ofthe actuator. Likewise, rotation of the motor shaft 22 in the oppositeor second direction results in axial movement of the thrust assembly andthus the fixture connection end 64 and attached fixture in an oppositesecond axial direction such as from the partially extended position ofFIG. 6 toward the retracted position of FIG. 2. Precise rotationalmovement of the motor shaft 22 and thus axial movement of the fixtureconnection end 64 and attached fixture is controlled via the rotaryencoder 77 together with appropriate control means (not shown). Suchcontrol means are well known in the art.

In the preferred embodiment, the actuator is generally provided with alead of about two millimeters (mm) to six millimeters (mm) andpreferably about four millimeters (mm). For purposes of the presentinvention, the “lead” as used in this context is the axial distancewhich the thrust assembly 46 and thus the connected fixture will advanceduring one revolution of the roller screw shaft 36. By reducing the leadfor a particular actuator, by increasing the thread density, acommensurate reduction in motor size can be made without jeopardizingany thrust. Although speed of movement may be jeopardized somewhat, thisis generally not a major issue. Accordingly, with a smaller lead, andthus a smaller motor, the entire package size of an actuator for a givenapplication can be reduced.

FIG. 10 shows a further embodiment of the actuator in accordance withthe present invention with a modified power connection end. As shown,the modified power connection end includes a distal portion 95 and aproximal portion 96. The proximal portion 96 includes a pair of recessedcorner sections 97,97. Positioned within the recessed sections 97,97 area pair of electrical connection posts or grommets 98,98. As shown, therecessed sections 97,97 are sufficiently large to totally enclose theconnection posts 98,98 and to prevent any portion of the posts 98,98from extending beyond the outer surfaces of the portions 95 or 96. Likethe cover 93, the modified connection end includes a plurality of holes80 to permit connection to the proximal bearing block 24.

The recessed connector post or grommet embodiment shown in FIG. 10 ispreferred, in some cases, over the embodiments of FIGS. 1 and 8 tobetter protect the connector posts and to prevent them from being rippedoff or otherwise damaged in collisions with robots or other machinery.The embodiment of FIG. 10 also provides flexibility for the electricalsupply cables to be connected so that they extend from the actuator inany orientation to best conceal the connections and keep them away frominterfering structure.

FIGS. 11, 12 and 13 show a modified manual override or means forpermitting the roller screw 36 to be manually rotated. This overridemeans includes a rotation member in the form of the toothed wheel oroverride gear 101 and an access opening 100. The wheel or gear 101 ismounted to a portion of the shaft extension 30 for rotation therewithand includes a plurality of teeth 102 positioned about its periphery. Asshown best in FIGS. 12 and 13, the gear 101 is formed of two halfsections 101 a and 101 b which are retained or clamped together formounting on the shaft section 30 by a pair of set screws 107. As shown,the outer diametrical dimension of the gear 101 is less than the widthof the chamber 48 and is axially positioned on the shaft section 30 sothat the wheel 101, and thus its peripheral teeth 102, are aligned withthe access opening 100. Preferably, the gear 101 is mounted on thedistal side of the bearing stop 103. The opening 100 is provided in oneof the sidewalls of the housing 42 and is sufficiently large to permit atool such as the end 104 of a screwdriver 105 to be inserted through theopening 100 for engagement with the teeth 102. In this manner, ifdesired, the tool 105 can be used to manually rotate the wheel 101 andthus the roller shaft 36.

To prevent dust and other contamination from entering the interior ofthe chamber 48 through the access opening 100, a closure means 99 isprovided to close the opening 100 during normal operation of theactuator. In the preferred embodiment, this closure means is in the formof a sliding window or gate 99 which is slideable between a closedposition shown in FIG. 10 and an open, access position shown in FIG. 11.As shown in FIG. 14, the closure means 99 is configured to be slideablein a slot or groove 114 in an exterior surface of one of the sidewalls43 and retained in a closed position by the set screw 115. To retain theclosure 99 in a closed position, the screw 115 is advanced against thegroove 114 as shown.

Accordingly, it can be seen that the actuator modification illustratedin FIGS. 10-14 includes a rotation member connected with the rollerscrew 36 and a selectively openable closure means for access to therotation member to permit manual rotation thereof.

Although the preferred embodiments of the present invention aredescribed with respect to a roller screw with planetary roller screws,it is contemplated that other means such as a ball screw or the like,among others, can also be used to convert the rotational movement of theroller screw shaft 36 into axial motion of the thrust tube assembly 46.

FIG. 16 shows a welding apparatus comprising the combination of awelding gun or fixture 118 with the actuator 10 of the presentinvention. Specifically, the welding gun or fixture 118 includes a pairof welding tips 116,116 which are pivotable about the pivot 119. Atleast one of the heads 116 is operatively connected to an actuation link120 which is turn operatively connected with the connection end 62(FIGS. 1, 2 and 6) of the actuator. As can be seen, although theactuation through the link 120 is generally linear, there can besignificant side loads applied to the actuator by the welding gun 118.This is due to the fact that the application of the load is offset fromthe longitudinal axis of the actuator and the link 120 moves through anarc. In the embodiment of FIG. 16, the welding gun 118 is connected tothe forward head 44 of the actuator by a plurality of cap screws.

Although the description of the preferred embodiment has been quitespecific, it is contemplated that various modifications could be madewithout deviating from the spirit of the present invention. Accordingly,it is intended that the scope of the present invention be dictated bythe appended claims rather than by the description of the preferredembodiment.

What is claimed is:
 1. An electrically powered actuator comprising: anelongated housing having a proximal end defined by a proximal end block,a distal end defined by a distal end block and a longitudinal axis; arotation shaft extending along said longitudinal axis and beingrotatably supported within and axially fixed relative to said housingand having a proximal end and a distal end; a thrust member having aproximal end and a distal end, said thrust member being concentric with,and axially moveable relative to, said rotation shaft and said housingalong said longitudinal axis, said thrust member further extendingthrough said distal end block, with the distal end of said thrust memberextending beyond and being axially moveable beyond said distal endblock; a coupling nut connected with said thrust member and moveabletherewith, said thrust member and said coupling nut being non-rotatablerelative to said housing; an electric motor having an output drive shaftextending therethrough, said drive shaft having a proximal end on oneside of said motor and a distal end on the other side of said motor,said output drive shaft being in-line and concentric with said rotationshaft, with the distal end of said drive shaft connected with theproximal end of said rotation shaft; and a rotary positioning encodermounted to the proximal end of said output drive shaft.
 2. The actuatorof claim 1 wherein said coupling nut is a planetary roller screw nut. 3.The actuator of claim 1 wherein the proximal end of said thrust memberis connected with said coupling nut and the distal end of said thrustmember is a free end for connection with a fixture.
 4. The actuator ofclaim 1 wherein the proximal end of said output drive shaft extendsthrough said encoder and includes a manually rotatable end.
 5. Theactuator of claim 4 including a head cover having an access opening tprovide access to said manually rotatable end.
 6. The actuator of claim5 wherein said access opening includes a selectively removeable plug toprovide selective access to said manually rotatable end.
 7. The actuatorof claim 1 including a motor housing having a distal end connected withsaid elongated housing and a proximal end and further including a headcover connected with the proximal end of said motor housing.
 8. Theactuator of claim 1 including an override rotation member connected toone of said rotation shaft and said drive shaft for rotation therewith.9. The actuator of claim 8 wherein said rotation member is an overridegear having a plurality of peripheral teeth.
 10. The actuator of claim 8including a selectively operable access opening in alignment with saidrotation member to provide manual rotation access to said rotationmember.
 11. The actuator of claim 1 including a bearing block positionedbetween said housing and said electric motor and a bearing mounted onsaid output drive shaft and within said bearing block.
 12. The actuatorof claim 11 wherein said rotation shaft includes a distal free endwherein said bearing includes a distal end and a proximal end andwherein one of said output drive shaft and said rotation shaft includesa bearing stop.
 13. The actuator of claim 12 wherein said distal end ofsaid bearing engages said bearing stop and said proximal end of saidbearing is retained by a bearing plate connected with said bearingblock.
 14. The actuator of claim 1 wherein said actuator includes adistal end and a proximal end and further includes an electrical supplyhead cover connected with said motor, wherein said head cover includesan exterior surface and first and second recessed portions and furtherincludes first and second electrical connector posts positioned in saidfirst and second recessed portions.
 15. The actuator of claim 1 whereinsaid bearing comprises at least one low friction disc.
 16. Anelectrically powered actuator comprising: an elongated housing having alongitudinal axis; a rotation shaft extending along said longitudinalaxis and being rotatably supported within said housing member; a thrustmember concentric with, and axially moveable relative to, said rotationshaft along said longitudinal axis; a coupling nut connected with saidthrust member and moveable therewith, said thrust member and saidcoupling nut being non-rotatable relative to said housing member; anelectric motor having an output drive shaft, said output drive shaftbeing in-line and concentric with, and integrally formed with saidrotation shaft; and a motor housing having a distal end connected withsaid elongated housing and a proximal end and further including a headcover connected with the proximal end of said motor housing, whereinsaid head cover includes a first head section and a second head section,said second head section being selectively connectable to said firsthead section in a plurality of positions.
 17. The actuator of claim 16wherein said second head section includes an external electricalconnection member.
 18. The actuator of claim 17 wherein said externalelectrical connection member is electrically connected with said motorregardless of the position of said second head section relative to saidfirst head section.
 19. An electrically powered actuator comprising: anelongated housing having a longitudinal axis; a rotation shaft extendingalong said longitudinal axis and being rotatably supported within saidhousing member; a thrust member concentric with, and axially moveablerelative to, said rotation shaft along said longitudinal axis; acoupling nut connected with said thrust member and moveable therewith,said thrust member and said coupling nut being non-rotatable relative tosaid housing member; an electric motor having an output drive shaft,said output drive shaft being in-line and concentric with, andintegrally formed with said rotation shaft; and a first bearing betweensaid coupling nut and a first portion of said housing and a secondbearing between said thrust member and a second portion of said housing.20. The actuator of claim 19 wherein said thrust member includes athrust tube with an exterior surface and said housing includes a tubehead and wherein said second bearing is positioned between a portion ofsaid tube head and said exterior surface of said thrust tube.
 21. Anelectrically powered actuator comprising: an elongated housing having alongitudinal axis; a rotation shaft including a distal free end,extending along said longitudinal axis and being rotatably supportedwithin said housing member; a thrust member concentric with, and axiallymoveable relative to, said rotation shaft along said longitudinal axis;a coupling nut connected with said thrust member and moveable therewith,said thrust member and said coupling nut being non-rotatable relative tosaid housing member; an electric motor having an output drive shaft,said output drive shaft being in-line and concentric with, andintegrally formed with said rotation shaft; and a bearing blockpositioned between said housing and said electric motor and a bearingmounted on said output drive shaft and within said bearing block whereinone of said output drive shaft and said rotation shaft includes abearing stop and wherein said bearing includes a distal end whichengages said bearing stop and a proximal end which is retained by abearing plate connected with said bearing block, wherein said bearingplate is connected to said bearing block by a plurality of threadedmembers.
 22. An electrically powered actuator comprising: a housinghaving a proximal end and a distal end; a rotation shaft within saidhousing and having a drive shaft portion extending toward the proximalend of said housing and a lead screw portion having a free end extendingtoward the distal end of said housing; an electrical motor connected todrive said drive shaft; a rotary encoder connected with said drive shaftnear the proximal end of said housing; an extendable and retractablethrust assembly surrounding said lead screw portion and having aproximal end located within said housing and a distal end extendingoutwardly from the distal end of said housing; a manual overriderotation member connected with said rotation shaft for rotationtherewith, said rotation shaft and said override rotation member beingaxially fixed relative to said housing; and an access opening in saidhousing to provide manual rotation access to said rotation member. 23.The actuator of claim 22 including a selectively openable and closeablecover for said access opening.
 24. The actuator of claim 22 wherein saidrotation member includes an override gear having a plurality ofperipheral teeth.
 25. The actuator of claim 24 including a selectivelyopenable and closeable cover for said access opening.
 26. Anelectrically powered actuator comprising: a screw actuator having aninline, direct drive electrical motor with a drive shaft having firstand second ends; a rotation shaft connected with the first end of saiddrive shaft and being driven by said motor; a rotary encoder connectedwith the second set of said drive shaft and being axially moveablerelative to said rotation shaft; an extendable and retractable thrustassembly having first and second ends; a housing surrounding said thrustassembly; and an impact relief assembly positoned between said rotationshaft and said thrust assembly and including a bumper of compressiblematerial and bearing means positioned between said rotation shaft andsaid thrust assembly.
 27. An electrically powered actuator comprising: ascrew actuator having an inline, direct drive electrical motor with adrive shaft having first and second ends; a rotation shaft connectedwith the first end of said drive shaft and being driven by said motor; arotary encoder connected with the second end of said drive shaft andbeing axially moveable relative to said rotation shaft; an extendableand retractable thrust assembly having first and second ends; a housingsurrounding said thrust assembly; and an impact relief assemblypositioned between said rotation shaft and said thrust assembly whereinsaid rotation shaft includes a distal end, and said thrust assemblyincludes a thrust tube having a distal end and wherein said impactrelief assembly is positioned between said distal end of said rotationshaft and said distal end of said thrust tube and includes a bumper ofcompressible material and a bearing member positioned between saidbumper and said distal end of said rotation shaft.
 28. A weldingapparatus comprising: an electric actuator having an elongated housingwith a longitudinal axis; a rotation shaft being rotationally supportedwith the housing; a thrust member having a proximal end and a distalfree end and being axially moveable relative to said rotation shaftalong said longitudinal axis, and an electric motor for rotating saidrotation shaft; a welding gun attached to said distal end of said thrustmember; an actuation link between said distal end and said welding gun;and first and second axially spaced bearing members positioned betweenportions of said thrust member and corresponding portions of saidhousing.
 29. The welding apparatus of claim 28 wherein said welding gunincludes at least one welding tip positioned offset from saidlongitudinal axis.
 30. An electrically powered actuator comprising: anelongated housing having a longitudinal axis; a rotation shaft extendingalong said longitudinal axis and being rotatably supported within saidhousing member; a thrust member concentric with, and axially moveablerelative to, said rotation shaft along said longitudinal axis; acoupling nut connected with said thrust member and moveable therewith,said thrust member and said coupling nut being non-rotatable relative tosaid housing member; an electric motor for driving said rotation shaft;and a first bearing between said coupling nut and a first portion ofsaid housing and a second bearing between said thrust member and asecond portion of said housing.
 31. An electrically powered actuatorcomprising: a screw actuator having an electrical motor for driving adrive shaft having first and second ends; a rotation shaft connectedwith the first end of said drive shaft; a rotary encoder connected withthe second set of said drive shaft; an extendable and retractable thrustassembly having first and second ends; and an impact relief assemblycomprising a bumper of compressible material and a bearing meanspositioned between said rotation shaft and said thrust assembly.